Marcello de Michele

Multisensor Satellite Monitoring of the 2011 Puyehue-Cordon Caulle Eruption

This paper shows the main outcomes of the Puyehue volcano (Chile) eruption monitoring by means of multisensor remote sensing instruments working from thermal infrared (TIR) to microwave (MW) spectral range. Thanks to the use of Synthetic Aperture Radar (SAR) and the Moderate Resolution Imaging Spectroradiometer (MODIS), the eruption evolution was observed, capturing the deformations of volcano edifice, the lava extension, as well as the information on ash and gas emitted. On the one hand, SAR Interferometry applied to ENVISAT-ASAR data allowed the estimation of the deformation occurred just before the beginning of the eruption and the subsequent deflation, with monthly sampling. On the other hand, with the combined use of the very high-resolution (VHR) images taken by COSMO-SkyMed X-band SAR, and ENVISAT-ASAR ones, we were able to follow the lava deposition during the most intense phase of the eruption. Additionally, the joined exploitation of SAR and optical MODIS images allowed ash detection, also in cloudy sky conditions. Finally, the information gathered by both types of sensors allowed to highlight some volcanological features of the eruption and the relationship between surface deformation and the amount of ash and gases emitted by the volcano.

Water depth inversion from satellite dataset

Within an effort to estimate near-shore bathymetry from satellite scenes, a method based on wave celerity and wavelength estimation is developed. These wave characteristics are extracted from SPOT-5 panchromatic and multispectral scenes. The method allows us to associate the wavelength and the celerity of the same detected wave and to estimate the water depth from the dispersion relation. This technique is tested on Saint Pierre area (La Reunion Island). Results are compared to in-situ measurements and show a reasonable agreement in terms of morphology and a mean absolute bathymetric error inferior to 30 % in intermediate depths (5-30 m range).

Revisiting the shallow Mw 5.1 Lorca earthquake (southeastern Spain) using C-band InSAR and elastic dislocation modelling

Space geodetic techniques such as interferometric synthetic aperture radar (InSAR) and global positioning systems (GPS) have demonstrated to be useful in mapping the displacement fields of large earthquakes (moment magnitude (Mw) ∼6 or higher). However, the displacement fields of smaller earthquakes (Mw < 5.5), such as those that typically result from the collision of the European and African plates, are less often analysed by space geodetic techniques, and their characterization, in terms of slip along the fault plane at depth and focal depth location, often challenges current seismological techniques. This letter presents the results of InSAR analysis of the 11 May 2011, Mw 5.1, Lorca earthquake. The Lorca earthquake occurred close to an area undergoing rapid subsidence due to sediment compaction related to water pumping. Therefore, it is challenging to separate the InSAR signals due to the earthquake from those due to human activity. We used four sets of SAR data acquired from the European C-band Advanced SAR (ASAR) sensor on board the Environmental Satellite (ENVISAT) to map the surface-displacement field in the Lorca region. Then, we use a simple elastic dislocation model to characterize the fault plane geometry and the fault slip at depth. We find that the InSAR signals can be explained by ∼21 cm reverse slip with a ∼6 cm left-lateral component on a 3 km × 3 km segment centred at 4.2 km depth dipping 45° NW and striking N65° E, consistent with the rupture of a segment of the Alhama de Murcia fault and consistent with recent published analyses. Interestingly, the InSAR signal can also be explained by ∼21 cm reverse slip with a ∼6 cm left-lateral component on a 3 km × 3 km segment centred at ∼4.2 km depth dipping 50° SE and striking N230° E, consistent with preliminary focal plane solutions indicating a rupture on a previously unmapped blind structure. We conclude that the second model cannot be rejected on the base of the InSAR results, the complex surface-displacement pattern (containing both seismic and non-seismic displacement), the different preliminary moment tensor solutions and the published locations of aftershocks at depth.

Water Depth Inversion From a Single SPOT-5 Dataset

Knowing bathymetry at intermediate depth, over large areas, and at a reasonable cost is a key issue. Spaceborne remote sensing techniques must play an essential role in retrieving such bathymetry. In this paper, a method is proposed that aims to address this issue without any in situ measurements by exploiting the characteristics of the SPOT-5 satellite dataset. The proposed method is designed to provide bathymetry from two optical SPOT-5 satellite images separated by a time lag DT of 2.04 s. It relies on the estimation of several clouds of wave celerity and wavelength pairs using wavelet and cross-correlation techniques and on the linear wave dispersion relation. This method has been applied to two SPOT-5 images on a test site characterized by complex bathymetry (Saint-Pierre, La Réunion Island). A comparison of the retrieved bathymetry with in situ bathymetric measurements reveals good morphological agreement. The mean relative error is less than 30% in the 3-80-m water depth range. The methodological choices made during method development are discussed based on additional computations, and guidelines for using the proposed method on other images at other sites are provided.

Observing water-level variations from space-borne high-resolution Synthetic Aperture Radar (SAR) image correlation

Abstract The potential of correlating high-resolution Synthetic Aperture Radar images to estimate local water-level variations is analysed based on observing the motions of floating structures. By computing range and azimuth offsets on a COSMO-SkyMed multi-temporal data-set in an area of the French Atlantic Coast, displacement signatures were detected in several harbours of the region. They can be associated with specific floating structures, whose vertical motion is mostly driven by tides. Although the image resolution is not the best achievable for the COSMO-SkyMed sensor, comparison with ground-based tide information revealed that the obtained space-borne measurements are consistent with the tide gauges to a decimetric accuracy. Even if the requirements for traditional users of tidal data are not met by the current revisit time of the COSMO-SkyMed constellation, the method proposed here provides complementary measures, which are already well aligned to requirements of users concerned with long-term sea-level variation and river or lake water stocks.

Potential of diffuse scatterer interferometry for monitoring CO2 storage sites in European contexts land cover types

This article proposes to test the feasibility of long-term surface deformation monitoring based on synthetic aperture radar (SAR) interferometry on carbon dioxide (CO2) storage sites with land cover representative of potential European injection sites (agricultural or forests with minimum built-up land cover). Because no operational injection site is currently active in Europe, a SAR data set (based on EnviSAT–ASAR spaceborne data) is simulated by combining SAR scenes acquired over a potential future European injection site with deformation measurements from SAR analysis carried out on the In-Salah (Algeria) CO2 injection demonstrator site. The study shows that under such conditions, both persistent scatterer interferometry (PSI) and diffuse scatterer (DS) interferometry appear insufficient to provide a sufficiently dense measurement network to characterize surface deformation correctly. Alternative solutions, to be investigated in further studies, include the use of data archives with shorter acquisition time spans (e.g. Sentinel-1 data when available) or installation of corner reflectors. The cost of the latter mixed space/ground solution must be evaluated with respect to conventional ground-based measurement methods in the proposed context.

Synthetic Aperture Radar (SAR) Doppler Anomaly Detected During the 2010 Merapi (Java, Indonesia) Eruption

In this letter, we report the presence of a localized Doppler anomaly occurring during the focusing of a Radarsat-2 data set acquired on the Merapi volcano (Indonesia) during the devastating 2010 eruption. The Doppler anomaly is manifested as ~ 3-km-wide bulls-eye-shaped azimuth pixel shifts between two subaperture images. The Doppler anomaly is centered on the summit-south flank of the Merapi volcano. The pixel shifts reach up to 11.6 m. Since the Merapi volcano was undergoing a large eruption during the data acquisition, it is possible that there is a volcano-related phenomenon that has delayed the radar signal so much to create measurable pixel offsets within a single synthetic aperture radar (SAR) data set, similar, but more extensive, to the signal generated by targets motions; similar, but less extensive, to the signal generated by ionospheric perturbations. It is known that the SAR signal is delayed as it passes through heterogeneous layers of the atmosphere, but this delay typically affects the SAR signal to a fraction of the phase cycle or few centimeters depending on the radar wavelength employed by the system. We investigate the source of this anomalous metric signal; we review the theoretical basis of SAR image focusing, and we try to provide a consistent physical framework to our observations. Our results are compatible with the SAR signal being perturbed during the actual process of image focusing by the presence of a contrasting medium located approximately between 6- and 12.5-km altitude, which we propose being associated with the presence of volcanic ash plume.

Shallow deformation of the San Andreas fault 5 years following the 2004 Parkfield earthquake (Mw6) combining ERS2 and Envisat InSAR

This study focuses on the shallow deformation that occurred during the 5 years following the Parkfield earthquake (28/09/2004, Mw 6, San Andreas Fault, California). We use Synthetic Aperture Radar interferometry (InSAR) to provide precise measurements of transient deformations after the Parkfield earthquake between 2005 and 2010. We propose a method to combine both ERS2 and ENVISAT interferograms to increase the temporal data sampling. Firstly, we combine 5 years of available Synthetic Aperture Radar (SAR) acquisitions including both ERS-2 and Envisat. Secondly, we stack selected interferograms (both from ERS2 and Envisat) for measuring the temporal evolution of the ground velocities at given time intervals. Thanks to its high spatial resolution, InSAR could provide new insights on the surface fault motion behavior over the 5 years following the Parkfield earthquake. As a complement to previous studies in this area, our results suggest that shallow transient deformations affected the Creeping-Parkfield-Cholame sections of the San Andreas Fault after the 2004 Mw6 Parkfield earthquake.

The Locking Depth of the Cholame Section of the San Andreas Fault from ERS2-Envisat InSAR

The Cholame section of the San Andreas Fault (SAF), which has been considered locked since 1857, has been little studied using geodetic methods. In this study, we propose to use Interferometric Synthetic Aperture Radar (InSAR) to contribute to the improvement of the knowledge of this section of the SAF. In particular, the objective of this work is to provide a description of the transition between the Parkfield and Cholame-Carrizo segments further southeast by producing an estimate of the locking depth of the Cholame segment by combining ERS2 (European Remote Sensing) and Envisat Advanced SAR (ASAR) satellites data. Our results indicate that the locking depth between the Parkfield and the Cholame-Carrizo segments deepens to the southeast. We then use these results as a hint to refine the tectonic loading on this section of the SAF.

Landslide displacement mapping based on ALOS-2/PALSAR-2 data using image correlation techniques and SAR interferometry: application to the Hell-Bourg landslide (Salazie Circle, La Réunion Island)

Abstract In the study described here, the capability of space-borne high-resolution L-band synthetic aperture radar (SAR) images (ALOS-2/PALSAR2 data in StripMap SM1 mode) for deriving and mapping two components of the deformation of slow landslides has been investigated. The deformation characterization was carried out on the basis of sub-pixel correlation offset tracking techniques and differential SAR interferometry. On the Hell-Bourg landslide (located on La Réunion Island, with displacements up to about 1 m/year), the deformation maps produced performed significantly better than the C-band or lower-resolution SAR data used in previous studies. A comparison was carried out with Global Navigation Satellite System data acquired on the test site. Even with a reduced image set (seven acquisitions), detailed deformation maps and information on deformation evolution during 2014–2016 could be generated. The combination of L-band data and high resolution was the source of the improved performance provided by this new kind of data.